Deflection apparatus

Abstract: The horizontal deflection apparatus has a separator the cross-section of which takes a saddle-shape form, and horizontal deflecting coils are comprised of three coil groups connected in a series to each other. The first coil group is wound on the outermost circumference on the inside of the main structure of the separator, the second coil group is wound at a predetermined distance from the first coil group, and the third coil group is wound at a predetermined distance from the second coil group. Deflecting efficiency at the deflection center is improved because the deflection magnetic field generated from the second and third coil groups is generated at the deflection center.

Description: The present invention relates to a deflection apparatus for a cathode ray tube that can be used with a horizontal deflection apparatus or a vertical deflection apparatus either of which uses groups of wound coils. A cathode ray tube (CRT) for a computer monitor or a television set uses a horizontal deflection apparatus as a means for deflecting a picture into a horizontal position. As illustrated in FIG. 1, the horizontal deflection apparatus has a saddle-shaped separator 10, inside of which groups of coils are wound separately into such saddle shape. Reference numeral 12 denotes the main structure of the separator which is made of resin and which has an upper bending portion 13 at its widest opening and a lower bending portion 14 at its narrowest opening. The horizontal deflecting coil groups 15 are wound separately around the upper bending portion 13 and the lower bending portion 14 in a predetermined area on the inside 12a (the side where the CRT is mounted) of the main structure of the separator 12, so as to be distributed in a predetermined manner. FIG. 2 illustrates a typical example. The horizontal deflecting coil groups 15 are arranged in a position having a predetermined number of turns inside the main structure of the separator 12a, wound around hooks 16a to 16f of the upper bending portion 13 and partitions 17a to 17c in the middle of the main structure of the separator 12. FIG. 3 is a schematic view illustrating the horizontal deflection apparatus 20 mounted on the CRT, which has an electron gun 22 in the neck 21a and the horizontal deflection apparatus 20 between the neck 21a and the funnel 21b. When receiving a sawtooth current, the horizontal deflection apparatus 20 scans and deflects an electron beam 23 horizontally onto a horizontal surface. Such deflecting apparatus is suggested in the U.S. patent application No. 832958 filed on February 10, 1992 by this same applicant (published as US5258734). However, it is necessary to reduce the dissipation power because the screen of the CRT is enlarged and increases the horizontal deflection power. It is also necessary to reduce the horizontal deflection power in order to improve the picture quality and to reduce costs. The horizontal deflection power PW is generally expressed in accordance with equation Eq1. PW = K x D 2 x HV x Sin 2 (0.5 x ) / 1 where K is the proportional constant, D is the diameter of the neck, HV is the CRT high voltage,  is the deflection angle (FIG. 3), and 1 is the magnetic path length of the horizontal deflection apparatus 20 (FIG. 3). It is also known that the horizontal deflection power PW can be determined in accordance with equation Eq2. PW = L x I 2 (mHA 2 ) where L is the inductance of the horizontal deflecting coil groups 15, and I is the deflection current. From Eq1, it is possible to solve the problem of reducing to greatest extent possible the horizontal deflection power PW, by (1) reducing the CRT high voltage HV, (2) reducing the diameter of the neck (the CRT 21 and the separator 10), (3) reducing the deflection angle , and/or (4) enlarging the magnetic path length 1. If the CRT high voltage HV is reduced, the luminance of the resulting picture is decreased because the speed at which the electron beam collides against the fluorescent screen 24 is decreased. If the diameter of the neck of the separator 10 and the CRT 21 is designed to be smaller, the diameter of the main electron lens in the electron gun 22 also becomes smaller, thereby causing the focus function and quality of the picture to deteriorate. If the deflecting angle  is reduced and the magnetic path length 1 is lengthened, the total length of the CRT 21 itself must also be lengthened and consequently the CRT becomes larger in size. Thus, it is inappropriate to change the horizontal deflection power PW that is represented by the equation Eq1 because such a change causes the picture quality to deteriorate and the CRT 21 to become longer. WO 93/20578 discloses a horizontal deflection apparatus for a cathode ray tube. It shows a saddle-shaped main coil group and an auxiliary coil group situated inside and in front of the main group. The auxiliary coil group carries current in the opposite sense to the main coil group so as to reduce the 4th Harmonics of the deflection field. Patent Abstracts of Japan, Vol. 17, No. 340 (E-1389) (JP5047319) discloses a vertical deflection coil set including an auxiliary coil pair wound inside the main coil pair so as to produce a magnetic flux in the same sense as the main coils in accordance with the preamble of claim 1. In accordance with the present invention, there is provided a deflection apparatus for a cathode ray tube comprising: a separator having a saddle-shaped cross-section; a first coil group wound around the inside of the outer circumference of said separator; a second coil group wound inside said first coil group, arranged at a predetermined distance therefrom; wherein said second coil group is connected to said first coil group and wound so as to increase, in use, the magnetic field strength at the centre of the deflection of the electron beam; and a third coil group wound separately apart from and inside of said second coil group. As shown in FIG. 11, the curved line La, representing the prior art, corresponds to the magnetic field strength at the center of the deflection of the electron beam and in the present invention it is increased to the level represented by the curved line Lb. Such increase of the deflecting magnetic field improves the horizontal deflecting efficiency without changing the other elements of the equation Eq1. This makes it possible to improve the picture quality and diminish the size by reducing the horizontal deflection power, while maintaining the quality of the picture from the prior art. The claims disclose the subject matter of the present invention. However, those skilled in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the following description with reference to the accompanying drawings wherein like reference characters refer to like elements. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective illustration of a separator; FIG. 2 is a frontal view (diagram) of a horizontal deflection apparatus currently in use; FIG. 3 is a cross-sectional view of a CRT currently in use; FIG. 4 is an frontal view (diagram) of one embodiment of a horizontal deflection apparatus according to the present invention; FIG. 5 is a perspective illustration of the relative positions of the first to third coil groups; FIG. 6 is an frontal view of an example of a separator used in FIG. 4; FIG. 7 is a cross-sectional view of line A-A from FIG.6; FIG. 8 is a cross-sectional view of line B-B from FIG.6; FIG. 9 is a cross-sectional view of line C-C from FIG.4; FIG. 10 is a cross-sectional view of a CRT using the horizontal deflection apparatus according to the present invention; FIG. 11 illustrates the distribution of the magnetic field in connection with FIG. 10; and FIG. 12 illustrates the positions of the first to third coil groups. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. FIG.4 illustrates the horizontal deflection apparatus 20 viewed from the side of the CRT funnel 21b as one embodiment according to the present invention. Horizontal deflecting coil groups 15 are divided into a plurality of coil groups. Of the horizontal deflecting coil groups 15 which are wound on the inside 12a of the main structure of the separator 12, the coil group which is wound around the outermost circumference is termed the first coil group 15a, which is in the same position as in the horizontal deflecting coil groups of the prior art. However, the number of times the coil is wound around the circumference is less than in the prior art. The second coil group 15b is wound on the inside of and at a predetermined distance from the first coil group 15a. The third coil group 15c is wound on the inside of and at a predetermined distance from the second coil group 15b. FIG. 5 illustrates the relative positions of the coil groups 15a to 15c so as to be easily understood by isolating the coil groups and emphasizing the distances between them. The number of loops for the second coil group 15b and the third coil group 15c are set to be 1/1 to 1/10 or more times the number of loops for the first coil group 15a, depending on the relationship between the space for winding and the deflecting magnetic field. In order to arrange in position the first to third coil groups 15a to 15c, the main structure of the separator 12 has hooks and partitions for arrangement as shown in FIG. 4. Referring to FIG. 4 and FIG. 6, the four hooks 16a to 16d are formed in positions such that each pair of hooks 16a and 16b, and 16c and 16d, are arranged respectively on the right and left sides at predetermined intervals and the three partitions 17a to 17c are formed in the middle of the outermost circumference, so as to arrange the first coil group 15a on the outermost circumference of the main structure of the separator 12. The hooks 16a to 16d are formed into the shapes illustrated in FIG. 7, and their width corresponds to the number of turns necessary for the coil. The long portions of the hooks separate the coil from the neighboring coils. The first coil group 15a is wound around the hooks 16a to 16d and the partitions 17a to 17c in saddle-shape form. As illustrated in FIG. 4 and 6, two hooks 31a and 31b are formed in the middle inside the main structure of the separator 12a where one hook is arranged on the right side, one hook is on the left side and three partitions 32a to 32c are formed between the hooks 31a and 31b. The second coil group 15b is wound around such hooks in a predetermined position. FIG. 8 is a cross-sectional view of the hook 31b. Three partitions 34a to 34c are formed for the third coil group 15c. Referring to FIG. 9, each of the partitions, 34a to 34c, is separated by small intervals in order not to interfere with the winding of the coils. The horizontal deflecting coil groups 15 (the upper horizontal deflecting coil groups) are comprised of the first, second and third coil groups 15a to 15c, which are connected in a series to each other, in such a way that the main structure of the separator 12 holds the second and third coil groups 15b and 15c inside at the middle. The horizontal deflection apparatus is comprised of the upper horizontal deflecting coil groups 15 and a lower horizontal deflecting coil groups (not shown) which have the same structure as the upper horizontal deflecting coil groups. FIG. 10 illustrates the above, and FIG. 11 illustrates the distribution of the magnetic field on the deflection center line P-P' from FIG. 10. The curved line La corresponds to the distribution of the magnetic field of the horizontal deflection apparatus of the prior art without the second and third coil groups, and the curved line Lb corresponds to the distribution of the magnetic field in the horizontal deflection apparatus according to the present invention. As clearly seen from the comparison of two curved lines La and Lb, the magnetic field strength is larger at the deflection center of the electron beam of the curved line Lb. The second and third coil groups 15b and 15c which are arranged at the deflection center contribute to the efficient generation of the magnetic field. The horizontal deflection power I can be increased with the deflecting current set at the same level as in the prior art. That is to say, the deflecting current I can be reduced, while generating the same level of the horizontal deflection power. Referring to FIG. 12, a concrete example is given as follows: first coil group : 55 turns second coil group : 6 turns third coil group : 9 turns inductance of horizontal deflecting coil L : 602.9mH distance between first and second coil group Lab : 1mm distance between second and third coil group Lbc : 1mm The total number of turns for the horizontal deflecting coil groups 15 is the same as in the prior art. When such horizontal deflection apparatus (DY) 20 is mounted in the CRT (28 inches), the horizontal deflection power PW is represented as follows: DY in Prior Art DY in The Invention Deflection Current I 8.61A 8.59A Deflection Power 49.1mHA 2 44.5mHA 2 As described above, the present invention can save 9.4% of the horizontal deflection power PW, as compared to the prior art. There could be many other examples of different numbers of coil groups, numbers of coils turns, and distances between the coil groups. It is also feasible to combine the first and second coil groups 15a and 15b or to combine the first and third coil groups 15a and 15c. When such deflection apparatus is used in a large CRT, it is more effective to arrange fourth and fifth coil groups inside the third coil group 15c. Although, in the embodiment, the present invention is applied to a horizontal deflection apparatus, it is feasible to apply the invention to a vertical deflection apparatus, which is also in a saddle-shape form. As described above, in the present invention, the deflecting coil groups must separate the second coil group from the first coil group on the outermost circumference of the separator. It is accordingly possible to distribute properly the magnetic field because the deflecting magnetic field at the deflection center of the electron beam is concentrated. This invention prevents the picture quality from deteriorating because the deflection efficiency can be improved without reducing the CRT high voltage and without reducing the diameter of the CRT neck. In this case, the CRT does not become larger because the deflection angle  and the magnetic path length 1 are the same as in the prior art. This invention is accordingly suitable for a CRT in a television set where it is necessary to reduce dissipation power.

Claims: A deflection apparatus for a cathode ray tube comprising: a separator (12) having a saddle-shaped cross-section; a first coil group (15a) wound around the inside of the outer circumference of said separator; a second coil group (15b) wound inside said first coil group, arranged at a predetermined distance therefrom; wherein said second coil group is connected to said first coil group and wound so as to increase, in use, the magnetic field strength at the centre of the deflection of the electron beam; characterised by a third coil group (15c) wound separately apart from and inside of said second coil group. A deflection apparatus according to claim 1 further comprising positioning means (16a-d, 17a-b, 31a and b, 32a-c) for locating the first and second coil groups in position on said separator. A deflection apparatus according to claim 2 wherein said positioning means is a hook or a partition. A deflection apparatus according to any one of claims 1 to 3, wherein said coil groups (15a-c) are connected in series to each other. A deflection apparatus according to any one of claims 1 to 4, wherein said coil groups are horizontal deflecting coil groups or vertical deflecting coil groups. A cathode ray tube display apparatus including a deflection apparatus according to any one of claims 1 to 5.

Inventors: KUMURA TOMOHIRO, OGAWA SEIICHI, KUMURA, TOMOHIRO, OGAWA, SEIICHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: H01J29
IPC codes: H01J29